Self-igniting rocket propellants containing organic silanes



United States Patent 3,028,272 SELF-IGNITING ROCKET PROPELLANTS CON- TAINING ORGANIC SILANES Pliny 0. Tawney, Passaic, N.J., assignor to United States Rubber Company, New York, N.Y., a corporation of New Jersey No Drawing. Filed Nov. 17, 1948, Ser. No. 60,618 7 Claims. (Cl. 149-36) This invention concerns self-igniting fuels for combustion machinery and more particularly relates to the use of certain chemical igniters for fuels which are based on a mixture of an organic material and an oxidizing agent. Such fuels, e.g., gasoline-nitric acid mixtures, have been employed in a variety of combustion machines and particularly in the jet propulsion type of engines, e.g., rockets. However, in such applications, these fuels require ignition either by an electrical or mechanical device or by chemical means.

This invention also relates to a new method of causing spontaneous ignition and to a new method of spontaneously igniting hydrocarbon fuels, particularly in rocket propulsion.

It has now been found that unsaturated organic silanes undergo spontaneous ignition when admixed with inorganic oxidizing agents, particularly those derived from nitrogen oxides, and it has been further discovered that such unsaturated silanes are particularly and unexpectedly efficacious as igniters for fuels based on mixtures of combustible organic materials and such inorganic oxidizing agents. This discovery is particularly surprising in view of the behavior of the corresponding saturated organic silanes which are relatively ineffective as igniters. Indeed even many of the unsaturated silanes containing atoms other than carbon, hydrogen and silicon, and particularly oxygen, nitrogen and sulfur are markedly inferior or completely useless for this purpose.

In practice, the blend of the combustible organic material and the unsaturated silane (preferably from 0.1 to 50% by Weight based on the organic fuel) is admixed in the combustion chamber of the engine with an appro priate oxidizing agent and ignition occurs instantaneously thereby initiating combustion of the fuel. Usually at least of the unsaturated silane based on the hydrocarbon is employed. The amount employed should be sufficient to efiect ignition. The amount required for ignition will depend upon the particular unsaturated silane used and can be readily determined by those skilled in the art in the light of this specification.

Since the use of these novel igniters obviates the necessity for a mechanical or electrical ignition system, the design and maintenance of the combustion machine is correspondingly simplified. Moreover it has been found that the use of these new chemical igniters introduce few or no additional problems such as corrosion, inflammability, toxicity, premature decomposition, etc. and hence propellant fuels based on these igniters can be employed in present installations and motors with little or no adaptation. Indeed the combustion reaction of my fuel deposits a protective refractory coating of finely divided silica on the walls of the combustion chamber, which retards the development of hot spots and other high temperature corrosion phenomena and thus prolongs the operational life cycle of the engine. This is particularly important in the art of jet propulsion since it permits sustained and protracted operation of such engines e.g., rockets, with a minimum of maintenance, repair and replacement.

The unsaturated silanes which are operable in this invention include both alkenyl and alkynyl silanes and the former are preferred. Of this class, the allylic-type silanes, i.e., those containing the group I I l I C=C-(|)-Sll are preferred on the basis of cost, availability and performance, particularly those silanes containing three or four of such allylic-type radicals e.g., allyl, Z-methylallyl, Z-ethylallyl and 3-methylallyl groups. This preferred group of silanes can be represented by the type formula -(R-CH=CR-CH ),,Si(R*)., where n is an integer having a value of 3 or 4, R and R are each one of the radicals, hydrogen and lower alkyl (e.g., methyl, ethyl) and R* is one of the radicals, hydrogen and alkyl (e.g., methyl, ethyl, propyl, isopropyl, butyl, isobutyl, amyl, hexyl, 2-ethylhexyl, heptyl, octyl, nonyl and decyl). R* is usually hydrogen or lower alkyl particularly methyl. Exemplary of such compounds are diallyl silane, tetra (Z-methallyl) silane, triallyl silane, tetraallyl silane, diallyl dimethyl silane, di(2-methylaliyl) dimethyl silane, allyl trimethyl silane and diallyl ethyl propyl silane. Tetraallyl silane and triallyl silane are especially preferred. These allylic-type silanes can be prepared by methods well-known to those skilled in the art, e.g., by the reaction of an allylic magnesium halide with a silicon halide.

The corresponding vinyl and isopropenyl silanes, e.g., divinyl silane, trivinyl silane and trivinylethyl silane are likewise operable but suffer the disadvantage of higher preparative costs. In addition to the above preferred class other unsaturated silanes include bis (trimethylsilyl) acetylene.

The above unsaturated silanes can be employed as igniters for a wide variety of combustible organic materials and inorganic oxidizing agents. Suitable combustible organic materials include those well-known to the art of jet-propulsion fuels such as hydrocarbons (e.g., propane, butane, butene, pentane, pentene-l, isopentane, cyclopentane, methylcyclopentane, hexane, isohexane, cyclohexane, heptane, octane, isooctane, mixtures thereof such as gasoline and kerosene, benzene, toluene and xylene), alcohols (e.g., methanol, ethanol, propanol, isopropanol, ethylene glycol, butanol and butanediol), ethers (e.g., dimethyl ether and dimethyl acetal), aldehydes (e.g., acetaldehyde, butyraldehyde and glyoxal), ketones (e.g., acetone, methyl ethyl ketone and butyl methyl ketone and acetophenone), amines (e.g., methyl amine, dimethyl amine, trimethyl amine, methyl ethyl amine, ethanol amine, aniline, N-methylaniline and p-phenylenediamine), hydrazines' (e.g., hydrazine, methyl hydrazine, dimethylhydrazine and phenylhydrazine). Among such organic materials the liquid compounds and/or mixtures thereof are preferred.

Among the inorganic oxidizing agents those derived from nitrogen oxides e.g., concentrated nitric acid, fuming nitric acid, nitrogen tetraoxide and mixtures of fuming nitric acid with sulfuric acid have proven satisfactory.

Some mixtures of the above fuels and oxidizing agents are themselves capable of spontaneous ignition, but even in such cases I have found that my unsaturated hydrocarbon silanes decrease the ignition time and improve the efficacy of such fuel mixtures, particularly with respect to the deposition of a protective silica deposit on the combustion chamber as described above.

The following examples disclose the invention in more detail.

EXAMPLE 1 The ignition ensuing from the reaction of the unsaturated silanes with various oxidizing agents derived from nitrogen oxides can be illustrated by adding 0.1 g. of the silane to 0.5 g. of the oxidizing agent. A number of these reactions are tabulated below (Table I) wherein the abbreviation Ig. signifies that ignition occurs while No Ig. means that no ignition is detected at the above concentrations.

combustion chamber in conjunction with the combustible organic fuel. The resulting mixture ignites spontaneously as soon as the materials are mixed.

The term inorganic oxidizing agent derived from an Table I oxide of nitrogen as used herein denotes either the oxides of nitrogen themselves, particularly nitrogen tetraoxide, oxidizing Agent and materials containing nitrogen tetraoxide especially turning nitric oxide, as well as materials containing the silane Red whit Wh te oxides of nitrogen in chemically combined form and ca- 253 fi f g f N20 f ig g i pable of releasing such oxides of nitrogen under the con- (sp,g (sp.g.= 12% ditions prevailing in the mixing chamber, for example, 1.59-1.00 1.40-1.50) H2504 concentrated nitric acid As used herein the term dispersion is used to denote g: the mixture of the unsaturated hydrocarbon silane and 1215121113 1 dimefliilsilzineII j- Ifilo %g... N I the combustible organic fuel whether such mixture be a o I in rr ii rh ii iiiiri n ii i rio Ig N3 15m No No 1g true solution or a collo1 da1 d1spers1on. (f) Tetrnethyl silane N0 Ig No Ig N0 Ig-.- N0 Ig I clalm as my nvent on:

1. A self-igniting fuel obtained by mixing an inorganic oxidizing agent derived from an oxide of nitrogen and F a g fig g i ii g ia 2 9g :3: 53383 3 0 selected from the group consisting of concentrated nitric gre acid, fuming nitric acid, nitrogen tetraoxide and mixtures allyhc substituents 1s increased. Moreover it W111 be of fuming nitric acid and Sulfuric acid with a liquid y noted that, in contrast, the saturated alkyl silanes of d I rocarbon having dispersed therein from 0.1 to 50% by 23 522 d'lsplay no igmuon' amvl'ty under these same weight of a poly-2-alkenyl silane of the type formula EXAMPLE 2 (R-CI-I=CR'-CH ),,Si(R*) where n is 3 or 4, R and R are each one of the radicals, hydrogen, methyl A number of the most active unsaturated silanes from ethyl one the TadiQaIS hydrogen and Table I above are employed as igniters for typical hydrogsz g gig 5 35 122232? Pt z s gf i h 11:33: 9 mlxmres by addfng a 2 A self-igniting fuel obt a i ned b mixin an nor a Solution of the silane in four representative hydrocarbon o d d f 1 Y g 1 8 me g .stsia fsiz aizzip .21.";saga tstaazaaai to g. o e oxi izing agent. e res ts, ta u ae below (Table II) are indicated by the same abbreviations gi i fig g f f E EE K animlgdures as g g n w e ........i.:.ti;t:. anatomist: tion g. meamng or er ne lgmtlon at at concentration has been added. The concentrations of the gg ig ii to 5 by Welght of a P l" silane in the hydrocarbon fuel are expressed in weight y S1 0 8 type ormula percent. 2)n *)4-n Table II Tetraallyl Triallyl Diallyl Ally] Oxidizing Agent Hydrocarbon silane, Cone. Silane, Cone. s gnimetchyl sffrimehyi i 0, one. 1 ane, one.

0350111100-- 0 1g 50.0 No Ig.

Benzene B- 79 50.0 No Ig. Red fuming s 5 lg 22.0 B. Ig 50.0 No Ig.

Xylene 20.0 B. Ig--"- 50.0 No Ig. aasolmenu 15 50.0 B. Ig."..- 50.0 No Ig...." 50.0 No Ig.

25.0 B. Ig 50.0 No Ig.. 50.0 No Ig. 22.0 B. Ig.-..- 50.0 No Ig----- 50.0 No Ig.

Xylene 28.0 B. Ig--.. 50.0 No Ig."-.. 50.0 No Ig. 30.0 B. T!

{35 0 30.0 B. Ig White turning HNO;

Tnlmmo Xylene 350Ig Gas01ine..- 350 White fuming HNO;,+12% Benzene..

H150 35.0 Ig

Toluene..-- y Xylene {2518 10m The principles of my invention may be employed wherever it is desired to effect spontaneous ignition. My

where n is 3 or 4, R and R are each one of the radicals, hydrogen, methyl and ethyl and R* is one of the radiinvention is particularly applicable in the field of jet procals, hydrogen and lower alkyl, said silane being present pulsion. In the usual application of my invention to jet propulsion, I provide separate supplies of the oxidizing agent derived from the nitrogen oxide on the one hand and of the unsaturated hydrocarbon silane on the other in an amount efiective to cause instantaneous ignition of the mixture.

3. A self-igniting fuel obtained by mixing an inorganic oxidizing agent derived from an oxide of nitrogen and hand and meter these materials continuously into the selected from the group consisting of concentrated nitric acid, fuming nitric acid, nitrogen tetraoxide and mixtures of fuming nitric acid and sulfuric acid with a liquid hydrocarbon having dispersed therein from 0.1 to 50% by weight of tetraallyl silane, said silane being present in an amount effective to cause instantaneous ignition of the mixture.

4. A self-igniting fuel obtained by mixing an inorganic oxidizing agent derived from an oxide of nitrogen and selected from the group consisting of concentrated nitric acid, fuming nitric acid, nitrogen tetraoxide and mixtures of fuming nitric acid and sulfuric acid with a liquid bydrocarbon boiling in the range of 75-300 C. having dispersed therein from 0.1 to 50% by weight of tetra allyl silane, said silane being present in an amount effective to cause instantaneous ignition of the mixture.

5. A self-igniting fuel obtained by mixing an inorganic oxidizing agent derived from an oxide of nitrogen and selected from the group consisting of concentrated nitric acid, fuming nitric acid, nitrogen tetraoxide and mixtures of fuming nitric acid and sulfuric acid with a liquid hydrocarbon boiling in the range of 75-300 C. having dispersed therein from 0.1 to 50% by weight of triallyl silane, said silane being present in an amount effective to cause instantaneous ignition of the mixture.

6. A self-igniting fuel obtained by mixing an inorganic oxidizing agent selected from the group consisting of concentrated nitric acid, fuming nitric acid, nitrogen tetraoxide, and mixtures of fuming nitric acid and sulfuric acid, a liquid combustible organic material selected from the group consisting of hydrocarbons, alcohols, ethers, aldehydes, ketones, amines, hydrazine, and substituted hydrazines, and from 0.1 to 50% by weight based on said liquid combustible organic material of a poly-2- alkenyl silane of the type formula where n is 3 or 4, R and R are each one of the radicals, hydrogen, methyl and ethyl, and R* is one of the radicals, hydrogen and lower alkyl, said silane being present in an amount efiective to cause instantaneous ignition of the mixture.

7. A propulsion fuel consisting of a liquid combustible organic material selected from the group consisting of hydrocarbons, alcohols, ethers, aldehydes, ketones, amines, hydrazine, and substituted hydrazines and from 0.1 to by weight based on said combustible organic material of a poly-2-alkeny1 silane of the type formula (R--CH=CR-CH ),,Si(R*) where n is 3 or 4, R and R are each one of the radicals, hydrogen, methyl and ethyl, and R* is one of the radicals, hydrogen and lower alkyl, said silane being present in an amount effective to cause instantaneous ignition of said fuel when it is admixed with an inorganic oxidizing agent selected from the group consisting of concentrated nitric acid, fuming nitric acid, nitrogen tetraoxide and mixtures of fuming nitric acid and sulfuric acid.

References Cited in the file of this patent UNITED STATES PATENTS 2,298,255 Hopkins Oct. 6, 1942 2,356,476 Shappirio Aug. 22, 1944 2,388,161 Kropa Oct. 30, 1945 2,474,183 King June 21, 1949 

7. A PROPULSION FUEL CONSISTING OF A LIQUID COMBUSTIBLE ORGANIC MATERIAL SELECTED FROM THE GROUP CONSISTING OF HYDROCARBONS, ALCOHOLS, ETHERS, ALDEHYDES, KETONES, AMINES, HYDRAZINE, AND SUBSTITUTED HYDRAZINES AND FROM 0.1 TO 50% BY WEIGHT BASED ON SAID COMBUSTIBLE ORGANIC MATERIAL OF A POLY-2-ALKENYL SILANE OF THE TYPE FORMULA (R-CH=CR''-CH2)NSI(R*)4-N WHERE N IS 3 OR 4, R AND R'' ARE EACH ONE OF THE RADICALS, HYDROGEN, METHYL AND ETHYL, AND R* IS ONE OF THE RADICALS, HYDROGEN AND LOWER ALKYL, SAID SILANE BEING PRESENT IN AN AMOUNT EFFECTIVE TO CAUSE INSTANTANEOUS IGNITION OF SAID FUEL WHEN IT IS ADMIXED WITH AN INORGANIC OXIDIZING AGENT SELECTED FROM THE GROUP CONSISTING OF CONCENTRATED NITRIC ACID, FUMING NITRIC ACID, NITROGEN TETRAOXIDE AND MIXTURES OF FUMING NITRIC ACID AND SULFURIC ACID. 